In a controlled trial of the effects of medical insurance on spending and health status, much less was spent on medical care when patients had to pay for it themselves. They economized by being less prone to seek treatment or be hospitalized for their illnesses. The average cost per hospitalization and per ambulatory episode was the same for all insurance plans.
Keeler EB, Rolph JE. How Cost Sharing Reduced Medical Spending of Participants in the Health Insurance Experiment. JAMA. 1983;249(16):2220-2222. doi:10.1001/jama.1983.03330400066026